1. Technical Field
The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile machine, and the like, and in particular relates to an image forming apparatus which forms a toner image corresponding to image data from an image forming unit including a rotary member and transfers the toner image onto a recording medium to obtain a finished image.
2. Related Art
Ever higher image quality continues to be demanded of image forming apparatus employing the electrophotographic method, and in particular preventing image density fluctuation within a single output image or a single page.
In general, image density fluctuation is caused by various factors, from charging to exposure, development, and transfer. Image density fluctuation occurs because the electric field that develops the image between the image carrier and the developer carrier is not constant but instead fluctuates due to the rotary oscillation or sensitivity fluctuation of the image carrier and rotary oscillation of the developer carrier, and consequently, the toner adhesion amount to be adhered on the latent image formed on the image carrier cyclically changes.
A conceivable approach is, for example, to periodically change the image forming conditions such as the developing bias voltage or charging bias voltage to cancel out any periodic fluctuation of the developing electric field, thereby reducing the image density fluctuation that occurs in the rotation cycle of the rotary members such as the image carrier and the developer carrier. For example, the image density fluctuation in the sub-scanning direction occurring in the rotation cycle of the image carrier can be measured in advance by forming a predetermined toner pattern, and the measurement result is stored in a memory so as to correspond to a phase of the image carrier. Then, the image density fluctuation data corresponding to the phase of the image carrier is read in printing the image, and the image forming condition is corrected based on the read data so as to cancel out the image density fluctuation occurring in the rotation cycle of the image carrier.
However, in this method, when the measurement error of the image density fluctuation data is high, the image forming condition capable of appropriately reducing the image density fluctuation that occurs in the rotation cycle of the image carrier cannot be set, and contrarily, the image density fluctuation is aggravated.
JP-2011-257497-A discloses an image forming apparatus capable of remedying the above adverse effect by forming an image for inspection to determine whether or not the banding correction is performed. However, the formation of the special toner pattern for inspection necessarily lengthens the processing time required for improving the image density accuracy and further, more toner needs to be consumed.